LONDON -- A coalition of environmental groups has called for a pivotal climate conference to be postponed amid concern that many of those most affected by global warming won't be able to attend because of the continuing threat from COVID-19.

Campaigners said Tuesday that organizers hadn't done enough to ensure broad participation in the event by providing access to vaccines and defraying the rising cost of travel for people from developing nations, many of which are subject to British government travel restrictions. The UN climate summit, known as is scheduled for Oct. 31-Nov. 12 in Scotland.

"Our concern is that those countries most deeply affected by the climate crisis and those countries suffering from the lack of support by rich nations in providing vaccines will be left out of the talks," said Tasneem Essop, executive director of Climate Action Network, which includes 1,500 groups in 130 countries. "There has always been an inherent power imbalance within the UN climate talks and this is now compounded by the health crisis."

But the Climate Vulnerable Forum, a group of 48 countries that are most at risk from climate change, later said an in-person summit must take place as scheduled to ensure the world responds to a threat "unparalleled in human history."

The tussle over postponement comes just weeks after an international panel of climate scientists issued a stark warning to world leaders, saying time was running out to avert the worst effects of climate change. COP26 is seen as a critical step in the drive to persuade governments, industry and investors around the world to make binding commitments on reducing greenhouse gas emissions.

The meeting was originally scheduled to be held last year, but it was postponed due to the pandemic.

"Clearly, every country needs to be given the opportunity to participate in COP26, but a further postponement at this stage could have very serious consequences by undermining the momentum for action on climate change," said Bob Ward, policy director for the Grantham Institute on Climate Change and the Environment in London.

The Climate Action Network, which includes groups such as Friends of the Earth and Amnesty International, called for postponement, saying organizers haven't done enough to ensure broad participation. Many of those countries are subject to British government restrictions that require travelers to undergo expensive testing and quarantines before entering the country.

But the Climate Vulnerable Forum, a grouping of the countries that are most at risk from climate change, said the summit should go ahead as planned in hopes of rebuilding international cooperating on combatting climate change.

"COP26 must happen in-person in October-November 2021 with robust COVID-19 measures ΓǪ." The group said in a statement. "This is the most important meeting for the future of the planet and it cannot wait."

The British government which is hosting the event rejected calls for postponement, saying leaders must tackle the issue of climate change without further delay.

"We are working tirelessly with all our partners, including the Scottish government and the U.N., to ensure an inclusive, accessible and safe summit in Glasgow with a comprehensive set of COVID mitigation measures," COP26 President-Designate Alok Sharma said in a statement.

World leaders, climate campaigners and activists from around the globe are due to attend the conference, which is expected to attract more than 20,000 people from almost 200 countries. Queen Elizabeth II and Pope Francis are among those expected to attend in person.

British officials are working on COVID-19 protocols for the conference that would ease travel restrictions for some delegates.

The rules may let both vaccinated and unvaccinated delegates from so-called red list countries enter the U.K. after a five-day period of self-isolation. More than 60 countries are currently on the government's red list because of concerns about infection levels. Most travel from these countries is banned, and those who do enter the U.K. are required to spend 10 days in a government-approved hotel at their own expense.

The discussion came on the day the European Union's climate monitoring service said average temperatures across the continent this summer were the warmest on record.

Measurements by the EU's Copernicus satellite monitoring program showed that June to August temperatures across Europe were about 1 degree Celsius (1.8 degrees Fahrenheit) higher than the 1991-2020 average, and 0.1 C warmer than the previous record recorded during the summers of 2010 and 2018.

Mediterranean countries in particular saw record-breaking temperatures this summer, along with devastating wildfires that prompted Greece this week to appoint a new minister of climate crisis and civil protection.

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Associated Press writer Frank Jordans in Berlin contributed to this report